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I use the version III on all of my filters as a prefilter. Such use has literally eliminated my need to ever open my canisters and I never have to clean the media in my HOB filters. Just great sponges and not a single one has ever failed. I have used some of the same sponges, rinsing when clogged, for years without issue. I could not issue a more hardy recommendation to use, in particular, the III prefilter!

Since I don't trust them yet, I use them as a pre-filter to auxillery wet-dry filtration along with other filtration forms. I don't know where others got thiers but I don't see them as cheap. The only fish stores I've found that use them exclusively have disease problems.